1. Field of the Invention
The present invention relates to an extruding method for manufacturing an elongate strip, such as an automotive molding, having at least one longitudinally extending hollow, cavity or lumen.
2. Description of the Prior Art
In some cases, moldings of rubber or resin are attached to the body of an automobile to protect the surface of the body and to provide a decorative effect. The molding, in general, is attached adhesively to the body by means of an adhesive film or with an adhesive.
Recently, a molding having a hollow or hollows has been developed in view of reducing the weight of the automobile. Such a molding tends to be decreased in strength because of the hollow hollows. To prevent a decrease in strength and an increase in weight, the hollow or hollows are filled with a foamed material or are partitioned by walls.
In manufacturing a molding having a partitioned hollow or hollows, an extruding die assembly having a partitioned cavity is used. Then, a material, such as a plasticized resin or rubber, is extruded through the cavity, and the extruded material is solidified to provide the molding. For example, as illustrated in FIGS. 6, 7 and 8, the extruding die assembly comprises a die 100 having an opening 101 defining the external shape of the molding, and an adapter 200 firmly holding the die 100 and mounted on an extruder (not shown) and a torpedolike core 300 held within the adapter 200 and having an outer end located within the opening 101 with the end surface thereof flush with the outer end surface of the die 100.
As illustrated in FIG. 6, the torpedo-like core 300 has a rear end divided into three parallel columnar sections 301 longitudinally extending and defining slit-shaped spaces 302 therebetween. Three parallel columnar sections 301 are extended from the end portion of the torpedo-like core 300 toward the rear end of the same.
The material extruded from the nozzle of the extruder flows through a space formed between the inner surface of the adapter 200 and the outer surface of the torpedo-like core 300 filling the slit-shaped spaces 302 formed between the columnar sections 301.
Part of the provided molding is a substantially T-shaped in transverse cross-section. The T-shaped part comprises head section in the form of a flat plate and leg section projecting from the middle of the head section. The leg section is the section formed by flow through the slit-shaped space 302. Therefore, the provided molding has two leg sections. Namely, the surface opposing the leg section of the T-shaped part corresponds to the surface of the molding, and the leg section corresponds to the wall which partitions the hollows.
In some cases, recesses deteriorating the external appearance of the molding are formed on the surface corresponding to the junction of the head section and the leg section of molding having partitioned hollows molded by the foregoing method. Although the causes of the formation of such recesses is not evident, it is inferred that such recesses are formed due to a subtle difference in the flow speed of the material between the portion of the cavity corresponding to the junction of the head section and the leg section, and the portion of the cavity corresponding to the head section or the leg section, because the volume of the extruded material in the portion of the cavity corresponding to the junction of the head section and the leg section is higher than that in the other portion of the cavity. Then, the inner stress becomes different between the junction of the head section and the leg section, and the other portion of the molding.